Blind Adaptive Constrained Constant-Modulus Reduced-Rank Interference Suppression Algorithms Based on Interpolation, Switched Decimation and Filtering

his work proposes a blind adaptive reduced-rank scheme and constrained constant-modulus (CCM) adaptive algorithms for interference suppression in wireless communications systems. The proposed scheme and algorithms are based on a two-stage processing framework that consists of a transformation matrix that performs dimensionality reduction followed by a reduced-rank estimator. The complex structure of the transformation matrix of existing methods motivates the development of a blind adaptive reduced-rank constrained (BARC) scheme along with a low-complexity reduced-rank decomposition. The proposed BARC scheme and a reduced-rank decomposition based on the concept of joint interpolation, switched decimation and reduced-rank estimation subject to a set of constraints are then detailed. The proposed set of constraints ensures that the multi-path components of the channel are combined prior to dimensionality reduction. In order to cost-effectively design the BARC scheme, we develop low-complexity decimation techniques, stochastic gradient and recursive least squares reduced-rank estimation algorithms. A model-order selection algorithm for adjusting the length of the estimators is devised along with techniques for determining the required number of switching branches to attain a predefined performance. An analysis of the convergence properties and issues of the proposed optimization and algorithms is carried out, and the key features of the optimization problem are discussed. We consider the application of the proposed algorithms to interference suppression in DSCDMA systems. The results show that the proposed algorithms outperform the best known reduced-rank schemes, while requiring lower complexity. his work proposes a blind adaptive reduced-rank scheme and constrained constant-modulus (CCM) adaptive algorithms for interference suppression in wireless communications systems. The proposed scheme and algorithms are based on a two-stage processing framework that consists of a transformation matrix that performs dimensionality reduction followed by a reducedrank estimator. The complex structure of the transformation matrix of existing methods motivates the development of a blind adaptive reduced-rank constrained (BARC) scheme along with a low-complexity reduced-rank decomposition. The proposed BARC scheme and a reduced-rank decomposition based on the concept of joint interpolation, switched decimation and reducedrank estimation subject to a set of constraints are then detailed. Copyright (c) 2010 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to [email protected]. This work was partially funded by the Ministry of Defence (MoD), UK, Contract No. RT/COM/S/021. Dr. R. C. de Lamare is with the Department of Electronics, University of York, York Y010 5DD, United Kingdom, Prof. R. Sampaio-Neto is with CETUC/PUC-RIO, 22453-900, Rio de Janeiro, Brazil and Prof. Haardt is with the Communications Research Laboratory, Ilmenau University of Technology, Germany. E-mails: [email protected], [email protected] and [email protected] The proposed set of constraints ensures that the multi-path components of the channel are combined prior to dimensionality reduction. In order to cost-effectively design the BARC scheme, we develop low-complexity decimation techniques, stochastic gradient and recursive least squares reduced-rank estimation algorithms. A model-order selection algorithm for adjusting the length of the estimators is devised along with techniques for determining the required number of switching branches to attain a predefined performance. An analysis of the convergence properties and issues of the proposed optimization and algorithms is carried out, and the key features of the optimization problem are discussed. We consider the application of the proposed algorithms to interference suppression in DS-CDMA systems. The results show that the proposed algorithms outperform the best known reduced-rank schemes, while requiring lower complexity. T